Resealable packages are widely used in the packaging of a variety of products, especially food. Resealable packages are convenient in that after the initial opening, consumers can close and reseal the package to better preserve the enclosed contents. Thus, a consumer avoids having to locate a storage container for the unused portion of the products in the package. As such, providing products in resealable packages appreciably enhances the marketability of those products.
Often, a resealable sealing device is produced as a separate item from the package and is attached to and made integral with the package at a later point in the manufacturing process. Air and water tend to migrate into the package at a higher rate near the sealing device. Two critical factors in preserving the contents in a resealable package include the integrity of the seal and the integrity of the region of the package at the interface of the sealing device. Thus, it is desirable to have a structurally sound bond at the interface between the sealing device and the package.
A typical resealable sealing device is a reclosable zipper which is affixed to the package by a heat and pressure sealing process. The zipper generally includes a pressure fastenable seal in the form of a rib, or male member, located on one package wall and a mating groove, or female member, located on an opposing package wall. To function as a reclosable zipper, the interlocking members of the closure arrangement should be made of a flexible polymeric material. The packages are also made of polymeric materials since these materials inhibit the migration of air and water from or into the package. The packages can be flexible or rigid.
Attaching a reclosable zipper to the package is fairly simple when both the zipper and the package material are made of compatible materials. By applying heat and pressure in the typical heat-sealing process, the zipper and package are made integral. A good example of this concept is a reclosable polyethylene sandwich bag utilizing a polyethylene zipper. Alternatively, in some arrangements, the packages and zipper devices are made from different materials. For example, packages made from polyester not only protect food from minor air and water losses but also minimize flavor scalping from food. But, these polyester packages often have polyethylene or polypropylene zippers. In this situation, a sealant layer between the zipper and the package is used which adequately bonds to both of the dissimilar materials. Thus, one side of the sealant layer bonds with the material of the zipper, while the other side of sealant layer bonds with the material of the package. Generally, the sealant layer is co-extruded with the closure device such that the sealant layer is bonded to the closure device. A method for co-extruding a sealant layer with a closure profile is disclosed in U.S. Pat. No. 5,242,516 issued to Custer et al. which is herein incorporated by reference. It has been shown that a complete sheet of sealant material generally cannot be co-extruded with the closure profile without causing the closure profile to become distorted after the two pieces are cooled due to the differences in the coefficient of thermal expansion.
When sealant layers are used, particular attention is placed on the heat-sealing process. To ensure an adequate bond, the dwell time and temperature of the heating process must be enough such that both sides of the sealant layer melt to their corresponding parts. Additionally, if the heat-sealing bar applying the heat load into the sealant layer becomes misaligned, then the sealant layer may not fully adhere to the zipper device or the package.
If the heat-sealing process is not performed adequately, the package will leak under the zipper device. And, when the consumer pulls the male closure portion away from the female closure portion to open the zipper, the imperfection could possibly enlarge. Thus, it is imperative that the bond is strong enough to resist tearing at this interface.
A need therefore exists to provide a structure at the interface between the closure profile and the package which further enhances the strength of the bond while still allowing the closure profile to be co-extruded with a sealant layer.